18 Feb 2014

3D printing is in fashion. Clothes, prosthetic limbs, guns
and even pizza, you name it—just about anything can be printed these days. Even
living cells.

Bioprinting is an emerging technology that promises to
revolutionise the field of regenerative medicine. The idea is simple: you load
a printer cartridge with cells removed from a patient or grown in the lab, and
then print a brand new tissue or organ ready for transplantation.
Alternatively, you could print healthy tissue directly onto a patient’s wound
in the operating room. For now, scientists and biotech companies have managed to
print several cell types, and there has been some progress in making cartilage,
skin and heart muscle tissue. Printed tissues like these could be invaluable
for drug testing in preclinical studies and for regenerative medicine. Imagine
if we could replace damaged brain tissue in people suffering from
neurodegenerative diseases like Alzheimers, or treat blindness with transplanted
eye tissue. But how does bioprinting work?

By a lucky coincidence, the size of the nozzles of
inkjet printers is roughly the same of an average animal cell, so scientists
can use or adapt commercial printers for bioprinting. Just like a conventional
3D printer, which creates objects by laying down liquefied material (like
plastic, metal or even chocolate) in layers, bioprinters work by spitting out
cell after cell onto a surface to, in theory, build a 3D-shaped living tissue. But
there is a caveat. Some cells are not happy to be squeezed through a printhead,
like neural cells for example, which have a limited ability to survive and grow
in culture.

Barbara Lorber and colleagues pushed a gel containing the cells
through a piezoelectric inkjet printer and then tried to grow them in culture
to test their survival rate. Piezoelectric printers are not commonly used for
bioprinting because they use an electrical pulse to eject the ink drops, and
this was thought to break cell membranes. But this is not what the team found. The
large majority of printed ganglion and glial cells were able to survive and
grow in culture. They also seemed to retain their function—glial cells released
growth-promoting molecules, and in turn ganglion cells responded to these
signals by growing more of the tiny processes that carry messages to neurons.

In recent years, stem cells transplants and electronic
retina implants were shown to partially restore sight in patients with retinal
degeneration, but these improvements were modest. Although preliminary, the new
results by the Cambridge team provide the proof-of-principle that the
production of functional retinal tissue by bioprinting could one day become a
reality.